[e2e] Estimating MS windows RTO equation

[Marco Mellia]

We are actually discriminating between 
- needed retransmission due to RTO
- unneeded retrasmission due to RTO (e.g., retransmitted packets already
acked by the client).
The second case may happen due to (but not only) spurious timeout
expiration. What is interesting is that unneeded retransmission almost
"disappear" if SACK is being used, hinting that they are more related to
"wrong" selective retransmit behavior rathern then wrong RTO
estimation...
If you want, you can read that as "spurios rto firing" is a very rare
event...


> Marco Mellia wrote:
> > 
> > We are working on the same topic, identifying packet anomalies (e.g.
> > retransmissions) in a TCP flow from passive measurement.
> > If you are interested, here are the links on the papers that we'll be
> > presented in June at ICC
> 
> 
> It would be interesting to see whether you will create a trace "what are
> spurious timeouts" in GPRS ;-) *SCNR*
> 
> To be serious: It would not be interesting to understand, what an SRTO
> really _is_, but it would be helpful to see, whether those practically
> occur.
> If you look at the technical report "TCP Spurious Timeout estimation in
> an operational GPRS/UMTS network" by 
> Francesco Vacirca, Thomas Ziegler and Eduard Hasenleithner, the authors
> do passive measurements of the particular anomalie "spurious timeout"
> and end up in the observation that these do hardly occur in reality. If
> this is correct, particularly the importance of SRTO
> has been drastically overestimated during the past few years.
> 
> So, what I think would be particularly interesting in a work like yours
> is that we are able to discrimate important problems from
> non important / neglectible ones.
> 
> It´s perhaps not that important to have an "OS identifying mechanism".
> IIRC there are quite a few papers around on this matter
> and to my understanding, this is more some kind of (necessary! and
> sophisticated!) debugging than "pure science".
> 
> However, it is very important to find out whether e.g. SRTO are reality
> or not. Spoken more drastically: If someone rides
> the SRTO horse once again, does he ride a dead horse?
> 
> This question is somewhat off topic for this thread, however I´m very
> interested in this topic. BTW: My personal expectation
> is that SRTO _ARE_ a dead horse.
> 
> Detlef
-- 
Ciao,                    /\/\/\rco

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